Facsimile data communication terminals have become quite popular for a variety of commercial, industrial, professional, governmental, and other applications. In many fields ready availability of facsimile communication is now considered to be essential.
Data communication by character transmission, as contrasted with the graphic transmission afforded by facsimile, is also virtually an essential requirement for many businesses, industrial plants, professional firms, governmental units, and others. In the past, data communication terminals of this kind have been incorporated into telex and TWX networks; more recently, transmissions of this kind have been carried out in accordance with DDD/ASCII transmission standards or Economy Telex standards, using conventional telephone lines. Indeed, even the telex and TWX networks may utilize public telephone lines for their transmissions in some instances.
For a business, a professional office, or other establishment where it is necessary or desirable to have both a facsimile terminal and a telex or DDD terminal, it has been necessary to employ two separate communication lines, with the attendant costs of installation and continuing monthly rental fees, even though both lines may be part of the same telephone network. This has been true even for offices and establishments that have relatively limited traffic which could easily be carried on a single communication line. There has been no generally available automated switching apparatus that could discriminate between incoming calls so as to make it feasible to operate both a facsimile terminal and a DDD/telex terminal on a single telephone line or other like communication line.
With increasing popularity of the use of computers as communication tools, particularly personal computers, a similar situation is developing for organizations that want to have data communication to distant locations both by a computer and by a facsimile terminal. To do so, it is usually necessary to have two telephone lines, with the attendant initial and continuing difficulties and expenses.